Re is an interjection commonly used in the greek language but also used in tha Balkans. It is used in speech to gain someone's attention, add emphasis, insult, or express surprise or astonishment, like the
Spanish che.
The
word probably comes from μωρέ, the vocative of the ancient Greek μωρός 'dull, sluggish, foolish, stupid'.
re is often accompanied by a slang
word but generally speaking you can use it any given sentence.